Kinnock added that he suspected Corbyn's wide appeal in the Labour party membership may be dwindling. "It remains to be seen how many members of the Labour party would support him in a vote," he told the BBC's Andrew Marr.

The former leader, who many see as kick-starting the process of reform which culminated in Tony Blair's landslide 1997 election victory, himself had to see off a leadership contest from Tony Benn in 1988. In that instance, Kinnock needed to secure nominations from MPs to get his name on the ticket for the ballot of party members. He said the same rules would still apply, meaning Corbyn would need the formal support of 50 MPs and MEPs.

However, the Labour leader this morning said he would stand in any contest and was "ready to reach out to Labour MPs who didn't accept my election and oppose my leadership - and work with the whole party to provide the alternative the country needs."